The standards of Singaporean journalism have slipped over the years...

Then again, this is the country that gave the world 'false statement of fact'.

As far as I can tell, the key to understanding that statement lies in the second half: "that the littering occurred from that residential flat."

This suggests that the investigator only has to prove in court that the litter came from a flat to charge the flat owners with an offense. He doesn't have to prove that the owners threw the litter. The owners have to prove that they didn't do it.